What to wear to a luau in Maui
Luaus in Wailea are relaxed but not scruffy: think a nice dinner out, adapted for a grass lawn by the ocean. The dress code is resort casual (Te Au Moana calls it smart casual). Here is what works, and what does not.

Outfit ideas
Women: a sundress or maxi dress, a flowy skirt with a light top, or linen trousers. Floral prints fit right in. Men: an aloha shirt or linen shirt with chino shorts or light trousers. Kids: whatever is comfortable and can survive a little haupia. Many guests buy an aloha shirt or dress on the island first; it is part of the fun. You will be given a lei or necklace at check-in, so you do not need to bring one.
Shoes, sun and the evening chill
Wear flat sandals or dressy flip-flops. Every Wailea luau is on a grass lawn, and reviewers mention a long walk from the parking structure at the Wailea Beach Resort, so heels are a mistake. The first hour of the evening is in full sun facing west: bring sunglasses and sunscreen. After sunset the trade winds pick up, so a light cardigan, wrap or overshirt is worth carrying, especially in winter.
What not to wear
Skip costume grass skirts, coconut bras and plastic leis: they imitate sacred hula attire and look out of place at a cultural show. Skip swimwear straight from the pool, heavy fabrics and anything you would hate to get a drop of teriyaki on. And do not overthink it: the evening itself is about food, music and the sunset. Once you are dressed, pick your show in the luau comparison.